Method and apparatus for providing ISDN access

ABSTRACT

ISDN access to a telecommunications network is provided to customers at different locations by sharing a D-channel controllers (DCC&#39;s) positioned within the network in close proximity to the ISDN-capable toll switches serving those customers. The customers provide call set up parameters to a DCC via a user interface system (UIS) at the customers premises that communicates via a dial-up data connection with a respective user support system (USS) connected to the DCC. The DCC in turn formulates ISDN signaling messages that are sent to the switch via a PRI interface and set up an appropriate communications path through the network to a desired destination. Data originating in customer premises equipment is received in the switch via a T1 access line operating in the &#34;non-facility associated signalling&#34; mode. Alternatively, a central USS located in a control center within the telecommunications network, transmits, via dial-up data connections, signalling information to individual USS&#39;s supporting associated DCC&#39;s.

FIELD OF THE INVENTION

This invention relates generally to Integrated Services Digital Network(ISDN) telecommunications systems, and, in particular, to method andapparatus for providing customers with the ability to generate signalingmessages necessary to support ISDN communications without the need for alocal D-channel controller (DCC).

BACKGROUND OF THE INVENTION

ACCUNET® switched 384 and 1536 digital data services available fromAT&T, and other similar services available from other inter-exchangetelecommunications carriers, are usage-sensitive dial-up digital dataservices capable of transporting 384 Kbps and 1.536 Mbps rate databetween customer presses locations. These offerings are well suited forsuch dial-up, i.e., on-demand, high speed data transmissionapplications, as bulk data transfer, computer graphics, enhancedteleconferencing, video communications, computer aided design, imagetransfer and retrieval, and so on.

Currently, customers obtain access/egress to the above-describedtransport services by, for example, using private lines between thecustomer presses and the inter-exchange carrier location. In a commonarrangement, access is provided via the ACCUNET® T1.5 service (alsoknown as T1 service), which includes 1.544 Mbps digital private linesthat are available from AT&T, and that use Primary Rate Interface (PRI)signaling. These private lines connect a toll switch (for example, a4ESS™ switch that supports Integrated Services Digital Network (ISDN)interface standards, with Customer Premises Equipment (CPE) that alsosupports the ISDN protocol.

While the foregoing arrangement is satisfactory for some customers, ithas some drawbacks, notably cost. In particular, in order to advise theISDN switch of information needed for routing, it is necessary for thecustomer to have interface equipment, generally known as a D-channelcontroller (DCC), to generate ISDN signaling messages based uponcustomer defined call set-up parameters. However, many customers cannotpresently afford to obtain the advantages associated with ISDN service,since the cost of a D-channel controller and a D-channel isprohibitively high.

In addition, the present arrangement is inefficient, because, in orderto obtain ISDN 1.536 Mbps functionality, a minimum of two 1.544 Mbps T1transmission lines are presently required. More specifically, a T1 linehas, in reality, somewhat less than 1.544 Mbps transmission capability,because of signaling overhead. Even if the full 1.544 Mbps capacity wereavailable, it would not be enough: the ISDN format requires a 1.536 Mbpstransmission channel, plus a 64 Kbps signaling channel, adding up tomore than the T1 capability. If two T1 lines are used for only one ISDNlink, the excess capacity (approximately 1.480 Mbps) is essentiallywasted.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, D-channelcontrollers are located within the telecommunications network,preferably in close proximity to each ISDN-capable toll switch. EachDCC, and the D channel between the DCC and its associated switch, isshared among customers at different locations. The DCC is accessed bysuch customers via a dial-up data connection, illustratively establishedbetween a user interface system (UIS) at the customer premises and auser support system (USS) connected to the DCC. When the DCC receivescall set up parameters from a customer, it generates ISDN signalingmessages that are transmitted to the associated toll switch via a PRIinterface on the shared D-channel, thereby establishing a communicationspath from customer's equipment through an ordinary T1 line operating inthe non-facility associated signaling (NFAS) mode to the switch, andthence to a desired destination.

Since each D-channel controller and its D channel are used in common bymultiple customers served by a given toll switch, and each DCC iscapable of controlling as many as 20 NFAS T1 links, large economies areeffected. In this way, customers can obtain a single T1 link for thepurpose of access, and use available switched digital services in orderto easily obtain "on-demand" switched telecommunications transmissioncapability.

In another embodiment of the present invention, a central USS is locatedin a control center within the telecommunications network, andcommunicates with each individual USS Supporting an associated DCC viadial up data connections. The central USS is accessed by customers indiverse locations via dial-up data connections, formulates signalingmessages based upon set-up parameters received from customer's UIS, andpasses these messages to the appropriate DCC, illustratively usinganother USS connected to the DCC. The DCC then formulates ISDN signalingmessages for transmission to the associated switch.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing,

FIG. 1 is a block diagram of a prior art telecommunications arrangementwherein signaling messages for digital traffic carded in one or morecommunication channels connecting customer premises equipment to an ISDNcapable switch are routed from a D-channel controller located at acustomer location to the switch via a PRI link;

FIG. 2 is a block diagram of one embodiment of our invention, in which aD-channel controller and a user support system (USS) are located inproximity to each toll switch in a communication network and used incommon by multiple customers served by each switch to set up switcheddigital communications channels over individual transmission facilitiesconnecting each customer to the associated switch;

FIG. 3 is a block diagram of a second embodiment of our invention, inwhich a central USS is located in a control center within thetelecommunications network, and communicates with the USS/DCCcombination located in proximity to each toll switch in the network;

FIG. 4 is a block diagram illustrating a typical arrangement for a userinterface system such as UIS 204-206 and 254-256 of FIG. 2;

FIG. 5 is a block diagram illustrating a typical arrangement for a usersupport system such as USS 222 and 272 of FIG. 2 or USS 322 of FIG. 3;and

FIG. 6 is a flow diagram illustrating a functional view of the processperformed in the system of FIG. 3.

DETAILED DESCRIPTION

Referring first to FIG. 1, there is shown a block diagram of a prior attelecommunications arrangement wherein a telecommunications customerhaving customer premises equipment (CPE) 102-104 at customer premises101 can communicate to distant locations, such as second customerpremises 151, via a switched digital communications network 150 usingthe ISDN protocol. While in FIG. 1, network 150 is shown as includingtwo ISDN capable switches 130 and 180 (which may be implemented as 4ESSelectronic switches available from AT&T) located within respectivePoints of Presence (POPs) 120 and 170, interconnected by a link 141, inactuality, network 150 may include additional switches. A description ofthe 4ESS switch is contained in Bell System Technical Journal (BSTJ)Vol. 56, No. 7, pp 1015-1320, September 1977.

Switches in network 150, including switches 130 and 180, are eachconnected to signal transfer points in a Common Channel Signaling (CCS7)network 140, which is a digital packet network arranged to carry CCS7signaling messages between switches. The CCS network is explained inBSTJ Vol. 57, No. 2, February 1978.

CCS7 signaling messages are originated in switches 130 and 180, basedupon ISDN signaling messages in PRI format received in each switch viaan input on the D-channel (shown as a dashed line) portion of accessline 114. The contents of ISDN messages, in turn, are based upon callset-up parameters (i.e., information derived from the calling and calledparties as well as information about desired bandwidth, etc.) The CCS7messages instruct switches 130 and 180 in network 150 to set up paths,such as link 141, so that communications originating in one customerpremises location can be extended to the desired endpoint ordestination.

Using network 150, a telecommunications customer can today obtaindial-up digital data service at 384 Kbps and at 1.536 Mbps rates,depending upon the type of information generated in CPE 102-104 and theprice that the customer is willing to pay for the communicationsservice. For many "communications intensive" applications such ascomputer communications and video processing, some CPE such as CPE 102and 104 may require the higher 1.536 Mbps rate, while other CPE such asCPE 103 may use a lower rate (384 Kbps) channel. In the case of theformer, at least two T1 digital access lines 114 and 115 are typicallyrequired between customer premises 101 and the switch 130 in the nearestPoint of Presence (POP) 120 within network 150 that serves thosepremises. In the example of FIG. 1, three access lines 114-116 areshown. At least two T1 lines are required because of capacitylimitations, and the fact that a 64 Kbps D-channel is required on atleast one of the access lines, in order to transport ISDN signalingmessages formatted in accordance with the PRI protocol. When thecapacity for D-channel signaling is allocated in, for example, accessline 114 (dashed line) the remaining capacity on line 114 is only 1.472Mbps (8 Kbps is required for framing purposes), which is insufficientfor the 1.536 Mbps rate required by CPE 102. Thus, CPE 102 must belinked to switch 130 via a separate T1 access line 115, using what iscommonly known as Non-Facility Associated Signaling (NFAS). CPE 104,also assumed to require 1.536 Mbps service, is linked to switch 130 viayet another T1 access line 116. Note that lines 115 and 116 need notinclude a D-channel for signaling; these lines support 24 channels, eachof 64 Kbps capacity, using what is commonly known as the D4 framingformat. Alternatively, the extended super frame (ESF) format, which ispreferred in the ISDN environment, can be used.

The NFAS concept will be understood by noting the presence in customerpremises 101 of D-channel controller (DCC) 110, which is connected toaccess line 114 via a multiplexer 111. DCC 110, which may be a PRImatesystem available from ISDN Technologies, Inc., or any similar product,prepares and encodes ISDN signaling messages in the 64 Kbps D-channel,and transmits these messages, formatted in accordance with the PRIprotocol, to switch 130. At the switch, the ISDN signaling messages arereceived and translated to CCS7 messages which are in turn transmittedto appropriate locations in network 150 via signaling network 140. The"primary" function of the ISDN signaling messages generated in DCC 110is to communicate with switch 130 in order to set up appropriate routingfrom that switch through network 150 for traffic such as 384 Kbps dataoriginating in CPE 103 that is applied to switch 130 via the 23 Bchannels remaining on the same access line 114 that contains the ISDNsignaling messages themselves. However, DCC 110 can also provide switch130 with ISDN signaling messages for traffic from "other facilities",for example, 1.536 Mbps traffic that is applied to switch 130 from CPE102 and 104 via access lines 115 and 116 that do not have their ownD-channel. This capability--signaling on one access line with respect totraffic on a different access line--is called non-facility associatedsignaling. Indeed, most D-channel controllers currently includesophisticated and relatively expensive circuitry arranged to generateISDN signaling messages that can be used to route traffic originatingfrom CPE connected to switch 130 via up to as many as 20 additional T1access lines. Without the present invention, these access lines had toserve a single customer location, i.e., customer premises 101.

If the arrangement in customer premises 151 is similar to thearrangement in customer premises 101 (i.e., DCC 160 provides ISDNsignaling in PRI format for CPE 153 via the D-channel in access line 164and NFAS ISDN signaling for CPE 152 and 154 via access lines 165 and166), CPE 102 (or 104) can communicate with CPE 152 (or 154) over atwo-way, switched digital 1.536 Mbps channel through network 150, usingNFAS signaling capabilities of both DCC 110 and DCC 160. In addition,CPE 103 (and other CPE requiting bandwidth available in access line 114)can communicate with CPE 153 over a two-way, switched digital 384 Kbpschannel through network 150, using DCCs 110 and 160 in their primarymode.

With the arrangement of FIG. 1, there is often excess, and therefore"wasted" capacity in the access lines connecting the customer premisesto the network. Also, the need for a separate D-channel and D-channelcontroller in each customer premises can be prohibitively expensive formany customers.

In FIG. 2, an arrangement in accordance with one embodiment of thepresent invention is illustrated in which a single D-channel controllerand a single D channel, is shared among many customers served by thesame toll switch and provides ISDN signaling messages for thecommunications channels (typically 24 B channels) that exist in theseveral access lines (which can originate in different locations)connecting each of those customers to the switch. As illustratedtherein, a first D-channel controller 223 is located within POP 220 inproximity to a first ISDN capable switch 230, and a second D-channelcontroller 273 is located within POP 270 in proximity to a second ISDNcapable switch 280. Other DCC's would be associated with other switchesin the network. DCCs 223 and 273 are connected to and receive inputsfrom respective user support systems (USS's) 222 and 272, and provideISDN signaling messages in PRI format to respective switches 230 and 280via the D-channel (dashed line) on T1 access lines 225 and 275. OtherPOPs within network 250, not shown, may be similarly configured.

In this arrangement, CPE in each customer premises is linked to theparticular ISDN capable switch serving that customer in a nearby POP, bya single T1 access line that does not include a D-channel. A userinterface system (UIS) in each customer premises is also linked to theDCC in the POP by an ordinary data (telephone) line. Thus, CPE incustomer premises 201-203 are linked to switch 230 in POP 220 by accesslines 211-213, respectively, and CPE in customer premises 251-253 arelinked to switch 280 in POP 270 by access lines 261-263, respectively.All of these access lines are typically T1 lines using D4 or ESFframing. Call set-up parameters needed to generate D-channel signalingmessages for communications originating at customer premises 201-203 aretransmitted to USS 222 in POP 220 from a particular UIS 204-206. Theconnection between UIS 204-206 and USS 222 may be ordinary voice gradetelephone lines 214-216, respectively.

Call set-up parameters originated in each customer premises 201-203, arereceived in USS 222 from the respective UIS 204-206, converted to ISDNsignaling messages in PRI format in DCC 223 and applied to switch 230via the D-channel portion of access line 225. Thus, a single D channelis shared by many customers. In switch 230, the received ISDN signalingmessages are converted to CCS7 messages and applied to signaling network240. This establishes the appropriate communication paths between thevarious switches in network 250, such that digital informationoriginated in customer premises 201-203 is routed (1) from customerequipment to the ISDN switch over an ordinary T1 line operating in theNFAS mode, and (2) from the switch via the telecommunications network toappropriate destinations, such as customer premises 251-253.

Note that in FIG. 2, customer premises 251-253 are likewise equippedwith UIS 254-256, each of which communicate with USS 272 via telephonelines 264-266, thereby controlling the routing of digital signalsapplied to switch 280 via T1 links 261-263, respectively.

By virtue of the advantageous arrangement of FIG. 2 wherein DCC 223 andthe D channel in access line 225 is shared by customers at multiplelocations including customer premises 201-203, each individual customercan obtain the benefits of ISDN communications without bearing theexpense of an individual D-channel or D-channel controller. In addition,each customer has an efficient access arrangement with respect to thenetwork: a single T1 facility to carry 1.536 Mbps traffic, and anordinary telephone line for UIS-to-USS signaling.

Referring now to FIG. 3, another embodiment of the present invention isillustrated in which a central user support system 321 is located in acontrol center 324 within telecommunications network 350. In thisarrangement, as in FIG. 2, CPE in customer premises 301-303 is connectedto the toll switch 330 serving that customer via respective T1 accesslines 311-313. These access lines do not have D-channels. UIS 304-306 ineach customer premises 301-303 communicates call setup parameters tocentral USS 321 typically via ordinary telephone lines 314-316. Callset-up parameters received from each UIS are processed in central USS321 in a similar manner as in the arrangement of FIG. 2, and passed tothe individual USS (e.g., USS 322) supporting an associated DCC (e.g.,DCC 323) located in close proximity to the switch serving the customer.The USS/DCC combination prepares appropriate ISDN signaling messages inPRI format in the same manner as described in connection with FIG. 2,and applies the messages to switch 330 via the D-channel on access line325.

In the arrangement of FIG. 3, central USS 321 in control center 324 alsosupports communications originated in customer premises (such ascustomer premises 351-353) connected to and served by other switches(such as switch 380) in other POPs (such as POP 370). Thus, a singlecentral user support system can support the entire network 350. However,for reliability or other purposes, it may sometimes be prudent toinclude several central USS's and/or several control centers withinnetwork 350. In any event, because of the shared use of central USS 321by customers served by several toll switches, it is desirable to utilizea customer data base (CDB) 327 in control center 324 to, for example,store information relating to the data rate associated with the calledparty number and the originating customer interface (T1.5), interpretcall set-up parameters received from various customer premises, andconvert the information to appropriate format before being applied toUSS 322 and DCC 323 (or to other USS's and associated D-channelcontrollers such as USS/DCC 372/373).

FIG. 4 is a block diagram illustrating a typical arrangement for a userinterface system such as UIS 204-206 and 254-256 of FIG. 2. Each UIS,located at a customer premises, may be a personal computer 401, a "dumb"(ASCII/synchronous) terminal, or any other processor that requires onlysimple resident applications software in order to receive, format andprepare to send to the USS, manually entered (e.g., via keyboard 403)parameters, specifically call setup and tear down information.Alternatively, UIS functionality may be incorporated in the customer'sapplication equipment, and programmed to automatically set up and teardown calls. A modem 402 providing a voice-band/data interface may beused to connect PC 401 in the UIS to the USS, so that call setup andtear down information generated in PC 401 in digital form can becommunicated to the USS over voice grade lines.

FIG. 5 is a block diagram illustrating a typical arrangement for a usersupport system such as USS 222 or 272 of FIG. 2, USS 322 or 372, orcentral USS 321 of FIG. 3. The USS, if based in a POP, may be anintegral part of the D-Channel Controller (DCC) or separate hardware.The USS contains processor hardware such as personal computer 501, andapplications software required to support the interface between the UISand the associated DCC such as DCC 503. A modem 502 forms the actualhardware interface between the USS of FIG. 5 and the remote UIS.Alternatively, software running on PC 501 can provide modem-likeinterfaces to multiple UIS's by, for example, processing inputs/outputsat multiple ports under common software control. Each modem, such asmodem 502, automatically answers calls from a UIS, and prompts thecustomer (using user friendly queries and responses) for call setup andtear down information, e.g., called party number, data rate, and lengthof call, etc. By storing appropriate data in PC 501, each USS cansupport customized calling capabilities for each customer, such asabbreviated "dialing". Other features that may be provided are callingparty number delivery, and call progress information during call setupand tear down. Information provided by the USS to the DCC is used toprepare ISDN PRI Q.931 protocol messages, which are sent to the ISDNswitch for call setup and tear down. As stated previously, the DCCtypically uses the ISDN PRI Non-Facility Associated Signaling (NFAS)capability to set up calls over the customer T1 access lines.

Because each USS may be used in common by multiple customers, certainsecurity functions may be included, such as prompting the UIS for acustomer login used to identify each customer, and for a password toprevent unauthorized users from accessing the USS. The supplied passwordmay be checked in an internal database associated with PC 501. Inaddition, USS software is preferably partitioned to prevent one customerfrom interfering with another customer's call(s) in progress, whichcould otherwise result in accidental setup and tear down. Partitionsbetween customers can also be based on the customer's login and/orpassword so that a separate customer profile can be provided for eachcustomer. The profile includes permissions and capabilities supported atthe customer's location.

If desired, the USS can also be remotely accessed by a "super user" foradministration purposes, e.g., for adding new customers. The USS maysupport "super user" access via a modem interface, or an ISDN temporarysignaling connection.

A functional view of the process performed using the arrangement of FIG.3 of the present invention is illustrated in FIG. 6. First, in step 601,a customer places a request for service by, for example, dialing intoUSS 321 using a predetermined 800 number. A suitable dialing interfaceis provided on personal computer 401 within the UIS of FIG. 4;alternatively, a dialing pad on a touch tone telephone may be used. Instep 602, service parameters are developed in USS 321. This is donethrough a dialogue between the USS and the customer, which requestsnecessary call set up information, including scheduled time for aconnection (if not immediate), location(s) to be connected, bandwidthdesired, billing options, reach number in case of set up difficulties,and, advantageously, duration (or ending time) of the desiredconnection. Customer identity validation and verification of resourceavailability may also be performed. The user interface personal computer401, provided by application software stored in memory, preferablypresents the customer with a visual display of choices, taking intoconsideration available customer facilities. Alternatively, an audiointerface would include a list of choices presented by a voice responseunit such as an AT&T Conversant system.

In step 603, signaling network 340 within communications network 350receives call set up information provided by the customer, which hasbeen appropriately formatted by DCC 323 and applied to switch 330 viaaccess line 325. An attempt is now made to actually set up the desiredcall. If successful, the process proceeds to step 604, otherwise thecustomer is informed of the problem or denial in step 605. The latterstep could include presentation, at personal computer 401, of anindication of the reasons for the denial, such as display of a messageindicating that the destination location is busy, insufficient capacityis available, terminating equipment is in a trouble condition, etc. Instep 604, service data is collected in network 350, so that, forexample, appropriate billing records can be formulated.

In step 606, DCC 323 monitors inputs from the customer to determine ifthe customer desires to change the previously specified terminationtime. In this manner, the customer is given the ability to terminate theconnection earlier than scheduled or extend it beyond the timeoriginally requested. If the customer has signaled the DCC withinformation indicative of such desire, the new information is stored inthis step. Thereafter, in step 607, DCC 323 monitors the storedtermination information to determine if termination should occur, i.e.,if the stored call termination time equals or exceeds the current time.If the termination time has not been reached, the connection continues;otherwise, termination occurs in step 608.

Various modifications and adaptations may be made to the presentinvention by those skilled in the art. For this reason, it is intendedthat the invention be limited only by the appended claims. For example,other signaling arrangements can be implemented between the customersand the shared DCC located in the network, and the ISDN switch served bythe DCC can be an intra-lata (local) ISDN switch or a PBX switch usingthe ISDN protocol, as well as a toll switch.

We claim:
 1. A system for providing signaling messages to ISDN capableswitches in a telecommunications network, said signaling messagescontaining information for routing ISDN calls connected to said switchesfrom a plurality of customers served by said switches to desireddestinations, said system comprisinga D-channel controller within saidnetwork; means for providing signaling messages derived from call set-upparameters generated by said customers to said D-channel controller, andmeans in said D-channel controller for formulating and sending to saidswitches ISDN signaling messages needed to set up appropriate pathsthrough said network to route said ISDN calls to said desireddestinations, wherein said providing means includes a processor forformatting said call set-up parameters and a modem for transmitting saidparameters to said D-channel controller over a voice grade telephoneline, and wherein said providing means further includes a processor forprompting said customers to enter individual elements of said callset-up parameters.
 2. A system for providing access to ISDN capableswitches in a telecommunications network, each of said switches servinga plurality of customers, said system comprisinga plurality of D-channelcontrollers within the network, each D-channel controller associatedwith a respective one of said switches; a respective user support systemconnected to each of said D-channel controllers, a user interface systemat the premises of customers served by each of said switches, means forproviding call set-up parameters generated in said customers premisesfrom said user interface system to the one of said user support systemsassociated with the switch serving said customer, via a dial-up dataconnection, means for communication a signaling message derived fromsaid call set-up parameters from said one user support system to itsrespective D-channel controller, means in said respective D-channelcontroller for formulating ISDN signaling messages and transmitting saidmessages to said switch serving said customer via a PRI interface, andmeans in said switch serving said customer for generating a signalingmessage needed to set up a communications path from the customer'spremises through the network to a desired destination.
 3. The inventiondefined in claim 2 further including means for providing dataoriginating in equipment at the customer's premises to said switchserving said customer via a T1 access line operating in the"non-facility associated signaling" mode.
 4. Apparatus for providingISDN control messages to switches in a telecommunications network, eachof said switches serving a plurality of subscribers, said systemcomprisingat least one D-channel controller within the network, eachD-channel controller associated with one of said switches; a userinterface system at the premises of subscribers served by each of saidswitches; a central user support system; means for providing call set-upparameters generated in said subscribers' premises from said userinterface system to said central user support system via a first dial-updata connection, means for communicating a signaling message derivedfrom said call set-up parameters from said central user support systemto the D-channel controller associated with the switch serving saidsubscriber, via a second dial-up data connection, and means in saidassociated D-channel controller for formulating ISDN control messagesand transmitting said control messages to said switch serving saidsubscriber via a PRI interface.
 5. The invention defined in claim 4wherein said system further includes a non-ISDN transmission link fortransporting data between said customers and the respective one of saidswitches serving said customers.
 6. A method for providing access toISDN capable switches in a telecommunications network, each of saidswitches serving a plurality of customers, said method comprising thesteps of:deploying at least one D-channel controller within the network,each D-channel controller associated with a respective one of saidswitches; providing call set-up parameters generated at the premises ofcustomers served by each of said switches from a user interface systemat said premises via a dial-up data connection, to a respective usersupport system connected to each of said D-channel controllerscommunicating information derived from said call set-up parameters fromsaid user support system to its connected D-channel controller;formulating ISDN signaling messages in said D-channel controller inresponse to said information; and transmitting said ISDN signalingmessages to said switch serving said customer via a PRI interface. 7.The method defined in claim 6 further including the step of providingdata originating in customer premises equipment to said switch servingsaid customer via a T1 access line operating in the "non-facilityassociated signaling" mode.
 8. A A method for providing ISDN controlmessages to switches in a telecommunications network, each of saidswitches serving a plurality of subscribers, said method of comprisingthe steps ofconnecting at least one D-channel controller to selectedones of said switches in said network; providing call set-up parametersin said subscribers premises from a user interface system at thepremises of subscriber served by a particular one of said switches to acentral user support system via a first dial-up data connection,communicating a signaling message derived from said call set-upparmeters from said central user support system to the D-channelcontroller associated with the switch serving said subscriber, via asecond dial-up data connection, formulating, in said associatedD-channel controller, ISDN control messages, and transmitting said ISDNcontrol messages to said switch serving said subscriber via a PRIinterface.